In this context, increasingly common is the use of glues instead of the more conventional techniques such as welding, above all as regards assembly of motor-vehicle bodies. Connection via glues enables, in fact, connection together also of non-metal parts and, consequently, enables introduction, in the composition of the body, of new materials, such as carbon fibres, fibreglass, and polymeric materials in general.
The process of gluing two components can also be accompanied by a process of supplementary fixing, for example a riveting process, in the case where, for specific applications, the glue alone is unable to provide the required forces of constraint. In these combined processes, the supplementary process, namely, application of the rivet in the example mentioned, is usually carried out in the same region of the two components in which the layer of glue has previously been applied. In effect, this layer of glue comes to affect the subsequent process, and this may give rise to problems regarding maintenance of a uniform quality of the pieces produced.